Min CPC size

[AndyPRK]

When a CPC is run on its own, what must the minimum size be ?


Its for a lighting circuit.


6m

 

[RF Lighting]

4.0mm² if not mechanically protected.

 

[AndyPRK]

So if its burred in plaster and not visible it can be smaller ?

 

[JohnW2]

So if its burred in plaster and not visible it can be smaller ?

The regs are not explicit about what constitutes adequate "protection against mechanical damage", but I somewhat doubt that they were thinking that burying in plaster would be adequate.

Even if so protected, it would still have to be 2.5mm², so, if you want to be sure that it's reg-compliant, and given that it's only 6m, it would probably be sensible to just use 4mm².

Kind Regards, John

 

[AndyPRK]

Fair comment, although I do have to get a 4mm into a light fitting!

 

[RF Lighting]

Why are you running a separate CPC anyway?

 

[AndyPRK]

old lighting circuit without CPC.

need to fit metal light.

not practical to replacing existing cable

 

[Taylortwocities]

Maybe a Class I luminaire being fitted on a non-earthed lighting circuit.?

 

[Risteard]

So if its burred in plaster and not visible it can be smaller ?

The regs are not explicit about what constitutes adequate "protection against mechanical damage"

I don't agree. If the cable is not insulated and sheathed nor run in containment then it cannot be described as mechanically protected. Therefore a 4mm^2 cpc would be required.

 

[AndyPRK]

so in conduit or trunking it can be smaller.

not sure about the insulated part though ?

 

[JohnW2]

The regs are not explicit about what constitutes adequate "protection against mechanical damage"

I don't agree. If the cable is not insulated and sheathed nor run in containment then it cannot be described as mechanically protected. Therefore a 4mm^2 cpc would be required.

I can't really see how you can disagree with my statement, since it is literally true that the reg in question is not explicit about what constitutes adequate "protection against mechanical damage". However, I do agree with what you are saying - as I wrote:

... but I somewhat doubt that they were thinking that burying in plaster would be adequate. ... it would probably be sensible to just use 4mm².

Kind Regards, John

 

[JohnW2]

so in conduit or trunking it can be smaller.

As I said, if it has adequate "protection against mechanical damage" (whatever that may be) it could be 2.5mm² (but no smaller). Proper metal conduit would certainly represent adequate protection - as for what lesser types of protection might be considered adequate, your guess is as good as mine.

not sure about the insulated part though ?

I presume the comment referred to the fact that you are presumably planning use cable which is not even "insulated and sheathed" (i.e. "double insulated"), although I wouldn't personally say that PVC sheathing represents significant 'mechanical protection'.

Kind Regards, John

 

[JohnW2]

Fair comment, although I do have to get a 4mm into a light fitting!

Yes, that's a problem. Even 2.5mm² could be difficult with some fittings. You may have to consider reducing it to, say, 1mm² for the last few inches to the fitting.

Kind Regards, John

 

[bernardgreen]

if you are going to get a 4 mm² CPC single pulled through might as well bite the bullet and replace the cable with twin and earth.

 

[AndyPRK]

well obviously I'm going to source the CPC from somewhere else that isn't a light circuit (let alone switched from its current position)


I think that is within the regs ?